The present invention relates generally to wireless communication systems and, more particularly, to a system and method for reducing blocking and abandonment of calls in a wireless communication system without increasing the number of channels employed.
The cellular industry has made phenomenal strides in commercial operations both in the United States and the rest of the world. Growth in major metropolitan areas has far exceeded expectations and is rapidly outstripping system capacity. If this trend continues, the effects of this industry""s growth will soon reach even the smallest markets. Innovative solutions are required to meet these increasing capacity needs as well as to maintain high quality service and avoid rising prices.
In addition to the challenges posed by the need for greater system capacity, the designers of future wireless communication systems have their own unique set of challenges. For example, one area of importance to system designers is to reduce the occurrence of call blocking (i.e., those instances when a call is attempted in a particular cell during a time when all channels in a cell are busy). Several attempts have been made to alleviate this problem. For example, one attempt is to simply signal to the calling party that all channels are busy (i.e., the calling party receives a busy signal). The busy signal tells the subscriber to attempt the call at a later time.
Another attempt is known as xe2x80x9cdirected retry.xe2x80x9d According to this conventional technique, when a cell site cannot handle a call from a wireless station (e.g., a cellular telephone or a mobile station) as a result of the site""s channels being busy, the cell site sends the wireless station a list of possible neighboring cell sites to which the wireless station can attempt to establish a connection. This, in effect, redirects the call to a neighboring cell site that can handle the call.
FIG. 1 is a flow diagram of a method for establishing a call using a conventional directed retry message. In FIG. 1, a subscriber attempts to establish a call through the use of a wireless station in a cell site of a wireless communication system (step 110). To establish the call, the wireless station scans for the strongest control channel and attempts to tune to it. In response, the base station of the cell site determines whether there are adequate resources available to handle the call (step 120). If the cell site has channels available to handle the call, then the cell site assigns an available channel to the wireless station (step 130) to complete the call. If, on the other hand, the cell site has no channels available, then, according to the conventional directed retry technique, the cell site sends a directed retry message to the wireless station (step 140).
The conventional directed retry message includes two fields: a reorder field and a retry list field. The reorder field indicates to the wireless station that no channels are available at the cell site to handle the call. The retry list field includes a list of neighboring cell sites to which the wireless station can attempt to establish a connection.
After receiving the conventional directed retry message, the wireless station scans for the strongest control channel in the retry list and attempts to establish the call at the neighboring cell site (step 150), thereby repeating the above-described process in the neighboring cell site. Wireless stations generally include a time-out feature. As such, if a call is not completed after a predetermined period of time, the wireless station considers the call attempt to have failed and indicates this to the subscriber. The time-out period is typically 6 to 30 seconds.
While this conventional directed retry technique reduces congestion in the cell site in which the call originated, it also increases the overall interference of the cellular network. This increased interference arises in both analog and digital systems.
In analog systems, for example, it will be appreciated that an assignment of a wireless station in a first cell to a base station in a second cell may interfere with the frequency management plan of the cellular network. Analog cellular networks generally implement a frequency reuse scheme. By directing a wireless station in a first cell to a control channel in a neighboring cell, interference with this carefully planned frequency scheme results.
In digital systems, the increased interference arise from at least two factors: (1) that the wireless station may be assigned a traffic channel from a relatively distant base station; (2) that the wireless station sends its communication on the traffic channel with a relatively high power level. Both of these factors negatively influence signal-to-noise ratios in the cellular network.
Therefore, there exists a need for a system and method that reduces blocking and abandonment of calls in a wireless communication system without increasing the number of channels employed or disrupting the frequency management scheme of the wireless system.
Systems and methods consistent with the present invention address this need by providing a retry feature that increases the number of successfully completed calls in a wireless communication system without increasing the number of channels employed or disrupting the frequency management scheme of analog networks.
A method consistent with the present invention includes receiving a call from a wireless station (e.g., a cellular phone) at a blocked cell site. In response thereto, the blocked cell site sends a retry message to the wireless station. The retry message directs the wireless station to effectively redial the call to the same cell site. After a natural delay period, the wireless station attempts to establish the call at the blocked cell site for a second time. If the cell site remains blocked, the above-described process is repeated until either adequate resources become available to complete the call, the subscriber hangs up, or the wireless station times out.
By continuously directing the call back to the blocked cell site, a virtual queue is effectively created. Viewed another way, a retry message consistent with the present invention creates for the subscriber an automatic redial feature where a block call is automatically redialed.
In another implementation consistent with the present invention, a computer readable medium includes a message data structure. The message data structure includes a reorder field that indicates that resources are unavailable and a retry field that directs a wireless device to retransmit a call request to an antenna of a cell site that originally received the call request.